Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For convenience, all heads that can read may be referred to as “read heads” herein, regardless of other devices or functions that the read head may also include or perform (e.g. writing, flying height control, touch down detection, lapping control, etc).
In a modern magnetic hard disk drive device, each read head is a sub-component of a head gimbal assembly (HGA). The read head typically includes a slider and a read/write transducer. The read/write transducer typically comprises a magneto-resistive read element (e.g. so-called giant magneto-resistive read element, or a tunneling magneto-resistive read element), and an inductive write structure comprising a flat coil deposited by photolithography, and a yoke structure having pole tips that face a disk media.
The HGA typically also includes a head suspension assembly that includes a mounting plate, a load beam, and a laminated flexure to carry the electrical signals to and from the read head. The read head is typically bonded to a tongue feature of the laminated flexure. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, a rotary actuator, and a flex cable. The mounting plate of each head suspension assembly is attached to an arm of the rotary actuator (e.g. by swaging), and each of the laminated flexures includes a flexure tail that is electrically connected to the HSA's flex cable (e.g. by solder reflow bonding or ultrasonic bonding).
Modern laminated flexures typically include electrically conductive copper traces that are isolated from a stainless steel support layer by a polyimide dielectric layer. So that the signals from/to the head can reach the flex cable on the actuator body, each HGA flexure includes a flexure tail that extends away from the head along the actuator arm and ultimately attaches to the flex cable adjacent the actuator body. That is, the flexure includes electrically conductive traces that are electrically connected to a plurality of electrically conductive bonding pads on the head (e.g. by solder jet bonding or gold ball bonding), and extend from adjacent the head to terminate at electrical connection points at the flexure tail.
The position of the HSA relative to the spinning disks in a disk drive, and therefore the position of the read heads relative to data tracks on the disks, is actively controlled by the rotary actuator which is typically driven by a voice coil motor (VCM). Specifically, electrical current passed through a coil of the VCM applies a torque to the rotary actuator, so that the read head can seek and follow desired data tracks on the spinning disk.
However, the industry trend towards increasing areal data density has necessitated substantial reduction in the spacing between data tracks on the disk. Also, disk drive performance requirements, especially requirements pertaining to the time required to access desired data, have not allowed the rotational speed of the disk to be reduced. In fact, for many disk drive applications, the rotational speed has been significantly increased. A consequence of these trends is that increased bandwidth is required for servo control of the read head position relative to data tracks on the spinning disk.
One solution that has been proposed in the art to increase disk drive servo bandwidth is dual-stage actuation. Under the dual-stage actuation concept, the rotary actuator that is driven by the VCM is employed as a coarse actuator (for large adjustments in the HSA position relative to the disk), while a so-called “milliactuator” having higher bandwidth but lesser stroke is used as a fine actuator (for smaller adjustments in the read head position). Various milliactuator designs have been proposed in the art for the purpose of dual-stage actuation in disk drive applications. Some of these designs utilize one or more piezoelectric milliactuators that are affixed to a component of the suspension assembly. For example, the piezoelectric milliactuator may be affixed to the mounting plate or an extension thereof, and/or the load beam or an extension thereof, or to the flexure tongue (a.k.a. the “gimbal tongue”) to which the read head is bonded.
Generally, the further the milliactuator is disposed from the read head on the suspension assembly, the less bandwidth it can provide. This is due to the dynamics introduced by the intermediate structure of the suspension assembly. On the other hand, the closer the milliactuator is disposed to the read head on the suspension assembly, the lesser stroke it can typically provide.
However, when the milliactuator is affixed to the mounting plate and/or to the load beam, the advantage of increased stroke may also be partially negated by failures and reliability concerns associated with mechanical stresses. Such mechanical stresses may result from handling or process steps during HGA and/or disk drive manufacture, or may result from exposure of the disk drive to mechanical shocks after manufacture. For example, as disk drive designs get thinner or/and disk drive applications require robustness to more severe mechanical shocks, HGA piezoelectric elements are becoming prone to undesired cracking. Such cracks may go undetected in screening and get incorporated into finished manufactured drives. Over time, such cracks in the piezoelectric elements may grow, and create loose particles. This may degrade both the performance and the reliability of the manufactured disk drives.
Therefore, there is a need in the information storage device arts for suspension assembly design improvements that can relieve or isolate mechanical stresses to piezoelectric subcomponents of a milliactuator, while still allowing an advantageous compromise between stroke and bandwidth for fine actuation of the read/write head.